Question

Q249. A uniform disc of radius R is spinned to the angular velocity ω and then carefully placed on a horizontal surface. How long will the disc be rotating on the surface if the friction coefficient is equal to k? The pressure exerted by the disc on the surface can be regarded as uniform.​

Answer 1

Here's your answer!

• Let's first assume the elemental area, dr.

• Let the area of that elemental area be dA.

Now, dA = 2πr.dr

And, elemental mass per unit area, dm = 2πr.dr × M/πr².

» dm = 2Mr.dr/πr²

And, dmg or dN = mg/πR² × 2πr.dr

» dmg or dN = 2Mgr.dr/R²

Now, as coefficient of friction is given as k.

Let's, consider it to be elemental.

» df = (dN) k

» df = 2MgK.dr/R²

[ Rest in the attachments ]

Hope it helps!

Answer 2

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